Intracardiac grasp catheter

ABSTRACT

A method of treating cardiac arrhythmia, including guiding a distal end portion of a catheter, the distal end portion having a distal tip and accommodating at least one elongated ablation electrode into a desired intracardiac region, for example, from the inferior vena cava into the right atrium of a human heart, and then from the right atrium into the right ventricle of the heart, pulling the catheter backwards, for example, towards the inferior vena cava, until the distal tip engages a edge of an intracardiac orifice, for example, the tricuspid annulus whereby the at least one ablation electrode engages a target tissue, for example, the isthmus of tissue between the tricuspid annulus and the inferior vena cava, deflecting the distal tip into a hook-shaped configuration, and activating the at least one ablation electrode to produce a substantially continuous lesion on the target tissue.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is continuation-in-part of U.S. patentapplication Ser. No. 09/434,599, filed Nov. 5, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 09/197,812,filed Nov. 23, 1998, all of which are incorporated by reference in theirentirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a steerable medical catheterand, more particularly, to a flexible, electrode-bearing catheter of thetype used in electrophysiological studies for intracardiacelectrocardiographic recording, mapping, stimulation and ablation.

BACKGROUND OF THE INVENTION

[0003] Catheters are often used in medical procedures to providephysical access to remote locations within a patient via a relativelysmall passageway, reducing the need for traditional invasive surgery.The catheter tube can be inserted into an artery or other passagewaythrough a relatively small incision in the patient's body, and threadedthrough the patient's system of blood vessels to reach the desiredtarget.

[0004] Various types of catheters are used in various procedures, bothdiagnostic and therapeutic. One general type of catheter used for bothdiagnostic and therapeutic applications is a cardiac electrode catheter.The diagnostic uses for a cardiac electrode catheter include recordingand mapping of the electrical signals generated in the course of normal(or abnormal) heart function. Therapeutic applications include pacing,or generating and placing the appropriate electrical signals tostimulate the patient's heart to beat in a specified manner, andablation. In an ablation procedure, electrical or radio-frequency energyis applied through an electrode catheter to form lesions in a desiredportion of the patient's heart, for example the right atrium. Whenproperly made, such lesions will alter the conductive characteristics ofportions of the patient's heart, thereby controlling the symptoms ofsupra-ventricular tachycardia, ventricular tachycardia, atrial flutter,atrial fibrillation, and other arrhythmias.

[0005] Such a catheter is typically placed within a desired portion ofthe patient's heart or arterial system by making a small incision in thepatient's body at a location where a suitable artery or vein isrelatively close to the patient's skin. The catheter is inserted throughthe incision into the artery and manipulated into position by threadingit through a sequence of arteries, which may include branches, turns,and other obstructions.

[0006] Once the cardiac electrode catheter has been maneuvered into theregion of interest, the electrodes at the distal end of the catheter areplaced against the anatomical feature or area sought to be diagnosed ortreated. This can be a difficult procedure. The electrophysiologistmanipulating the catheter typically can only do so by operating a systemof controls at the proximal end of the catheter shaft. The catheter canbe advanced and withdrawn longitudinally by pushing and pulling on thecatheter shaft, and can be rotated about its axis by rotating a controlat the proximal end. Both of these operations are rendered even moredifficult by the likelihood that the catheter must be threaded throughan extremely tortuous path to reach the target area. Finally, once thetip of the catheter has reached the target area, the electrodes at thedistal end of the catheter are placed in proximity to the anatomicalfeature, and diagnosis or treatment can begin.

[0007] In the past, the difficulties experienced by electrophysiologistsin the use of a cardiac electrode catheter have been addressed in anumber of different ways.

[0008] To facilitate maneuvering a catheter through a tight and sinuoussequence of arterial or venous passageways, catheters having apre-shaped curve at their distal end have been developed. To negotiatethe twists and branches common in a patient's arterial or venous system,the catheter typically is rotatable to orient the pre-shaped curve in adesired direction. Although the tip of the catheter may be somewhatflexible, the curve is fixed into the catheter at the time ofmanufacture. The radius and extent of the curvature generally cannot bealtered. Therefore, extensive pre-surgical planning is frequentlynecessary to determine what curvature of catheter is necessary. If thepredicted curvature turns out to be incorrect, the entire catheter mayneed to be removed and replaced with one having the proper curvature.This is an expensive and time-consuming ordeal, as catheters aregenerally designed to be used only once and discarded. Moreover, theadditional delay may place the patient at some additional risk.

[0009] A variation of the pre-shaped catheter uses a deflectable curvestructure in the tip. This type of catheter has a tip that is ordinarilysubstantially straight, but is deflectable to assume a curvedconfiguration upon application of force to the tip. However, the tipdeflection is not remotely controllable. In a certain patient's arterialsystem, a point may be reached at which the proper force cannot beapplied to the catheter tip. In such cases, the catheter must bewithdrawn and reinserted through a more appropriate passage, or anothercatheter with a different tip configuration must be used.

[0010] Another attempt to facilitate the placement of catheters takesthe form of a unidirectional steering catheter. A typical unidirectionalsteering catheter has a steering mechanism, such as a wire, that extendsthe length of the catheter to the distal tip. The steering mechanism iscoupled to the tip in such a way that manipulation of the proximal endof the mechanism (e.g., by pulling the steering wire) results indeflection of the catheter tip in a single direction. This type ofcatheter is illustrated, for example, in U.S. Pat. No. 5,125,896 issuedto Hojeibane. The direction of deflection can be controlled by embeddinga ribbon of wire in the tip; the ribbon is flexible along one dimensionbut not in others. This type of catheter can further be controlled byrotating the entire shaft of the catheter; in this manner, the directionof bend within the patient can be controlled. The shaft of such acatheter must be strong enough to transmit torque for the latter form ofcontrol to be possible.

[0011] U.S. Pat. No. 5,383,852 to Stevens-Wright describes a steerableelectrocardial catheter including a flexible tip assembly having aproximal and a distal section. In this catheter, two steering mechanismsare used to separately control bending of either or both the proximaland distal sections. The steering mechanisms for the proximal and distalsections include separate steering wires, as described above, which arecoupled to the proximal and distal sections, respectively.

[0012] Bidirectional steering catheters also exist. The distal end of abidirectional steering catheter can be maneuvered in two planes,allowing the tip to be positioned with greater accuracy. However,bidirectional steering catheters are complex mechanically and are oftendifficult to manipulate.

[0013] Although the foregoing types of catheters address the issue ofmaneuverability in different ways, none of them is ideally configured tomaintain contact with and apply a desired amount of pressure to adesired anatomical feature, such as an atrial wall.

[0014] One device used for the latter purpose is known as a basketcatheter. See, for example, the HIGH DENSITY MAPPING BASKET CATHETERmanufactured by Cardiac Pathways Corporation. A basket catheter hasseveral spring-biased arms near the distal tip. When these arms areunconstrained, they bow outward to define a basket-like shape. The armsof the basket are constrained for implantation in a sheath structure.When the tip of the catheter has reached the desired location, thesheath is retracted, or the arms are advanced out of the sheath.

[0015] However, because the tip of the catheter is sheathed, it is noteasily steerable into location, and is not as flexible as one mightdesire. Moreover, the sheath adds bulk to the device, which mightsignificantly limit the range of applications in which the basketcatheter can be used. The basket has only one shape and size. Once thearms are deployed from the sheath, the basket assumes a singleconfiguration defined upon manufacture. If the predefined configurationof the basket is not suitable, then substantially no correction ispossible. Also, known basket catheters are not indicated for use inhigh-energy therapeutic applications, such as ablation.

[0016] A variable-geometry sheathed electrode catheter is also known inthe art. This device has a single electrode-bearing tip portion that isinitially disposed within a relatively inflexible sheath. When the tipportion is advanced with respect to the sheath, the tip portion bows outof a slot-shaped aperture in the sheath. The shape of the tip portioncan be controlled to apply a desired amount of pressure to an anatomicalfeature. However, as a sheath is used around the catheter, the device isnot easily steerable into location. Moreover, as discussed above, thesheath structure adds undesirable bulk to the device.

[0017] Radio frequency ablation (RFA) has become the treatment of choicefor specific rhythm disturbances. To eliminate the precise location inthe heart from which an arrhythmia originates, high frequency radiowaves are generated onto the target tissue, whereby heat induced in thetissue burns the tissue to eliminate the source of arrhythmia.

[0018] For successful ablation treatment, e.g., to produce a lesion at agiven anatomical site, it is generally required that the catheter beaccurately positioned at the ablation site and that continuous contactbe maintained between the electrode and the ablation site for theduration of the ablation treatment.

[0019] U.S. Pat. No. 5,617,854 to Munsif describes, inter alia, apre-shaped catheter particularly useful for ablating in the vicinity ofthe sinoatrial node, the left atrium, and up to the mitral valve. Thetip of the catheter is formed of a temperature-sensitive shape-memorymaterial, e.g., Nitinol, or is otherwise invoked to assume a segmentedconfiguration upon reaching a desired position. The segmentedconfiguration includes a distal segment which bears an ablationelectrode. In operation, the segmented shape produces tension whichurges the ablation electrode on the distal segment into contact with awall of the left atrium, while other segments are urged against othertissue. Since the shape of the catheter tip is fixed, the tip is noteasily manipulated. Further, the tension produced between the segmentsof the catheter tip is dependent on the shape and dimensions of theablation site, e.g., the left atrium.

[0020] Atrial fibrillation and atrial flutter are the most common typeof arrhythmia found in clinical practice. Although the potential adverseconsequences of these types of arrhythmia is well known, the basicelectrophysiological mechanisms and certain management strategies tocontrol these types of arrhythmia have been understood only recently.

[0021] Reference is made to FIG. 1 which schematically illustrates across-section of a human heart 100 showing typical atrial fluttercircuits. Such circuits includes macro-entrant, counter-clockwise,pathways 120 from the right atrium 102, through the inter-atrial septum114, down the free wall 116, and across the isthmus of tissue 108between the inferior vena cava 112 and the tricuspid annulus 106 of thetricuspid valve 110.

[0022] Most electrophysiologists recommend treating atrial flutter byproducing a linear contiguous lesion 118 at the isthmus of tissue 108,between vena cava 112 and the tricuspid annulus 106. Linear lesion 118can be produced by RF ablation electrodes which are placed in contactwith tissue 108. It is contemplated that isthmus tissue 108 is acritical link of the atrial flutter circuit and, thus, linear lesion 118is expected to terminate this source of arrhythmia and prevent therecurrence of such arrhythmia.

[0023] Existing ablation treatment for atrial flutter includes the useof a catheter bearing at least one single or bi-polar ablationelectrode. Unfortunately, an undue amount of time is spent in correctlypositioning the ablation electrode of the catheter against the site tobe treated. Further, in existing electrode catheter configurations, thecatheter must generally be repeatedly repositioned until an acceptablelesion 118 is produced. Thus, lesion 118 is often non-continuous, i.e.,there may be gaps in the lesion line which may require furtherrepositioning of the ablation catheter. Such repeated repositioning ofthe catheter is time consuming and may result in prolonged, potentiallyharmful, exposure of patients to X-ray radiation.

[0024] Accordingly, there is a need for a cardiac electrode catheterthat can be conveniently and quickly steered into secured, operative,engagement with a preselected portion of the isthmus of tissue betweenthe inferior vena cava and the tricuspid annulus, to produce apredefined, substantially continuous, lesion on this isthmus of tissue.

[0025] The difficulties in steering, positioning and providing securedcontact of an electrode catheter, with reference to the isthmus oftissue between the interior vena cava and the tricuspid annulus, arealso applicable in mapping and/or ablating other intracardiac sites. Forexample, steering and positioning difficulties may arise in mapping andpossible ablation in the vicinity of the coronary sinus.

SUMMARY OF THE INVENTION

[0026] The present invention seeks to provide a steerable electrodecatheter having a relatively flexible distal end portion accommodatingan elongated configuration of at least one ablation electrode, that canbe conveniently guided to a predetermined intracardiac site, forexample, to the vicinity of the tricuspid valve, and that can be steeredinto a shape which enables convenient positioning of at least oneablation electrode in secure operative engagement with predeterminedmapping and/or ablation site, for example, an ablation site along theisthmus of tissue between the inferior vena cava and the tricuspidannulus. If ablation of tissue is required, an electrode catheter inaccordance with the present invention may be used to produce apredefined, elongated, substantially continuous, lesion at the ablationsite.

[0027] According to an embodiment of the present invention, the catheterincludes a flexible distal end portion which may be controlled by one ortwo steering mechanisms, namely, a distal steering mechanism and/or aproximal steering mechanism. The distal steering mechanism may beadapted to deflect only the tip of the distal end portion into ahook-shaped configuration. The proximal steering mechanism may beadapted to deflect the entire distal end portion. Alternatively, thedistal end portion of the electrode catheter may have a pre-shapeddistal tip, e.g., the tip may be pre-shaped into a partly deflectedconfiguration. In this alternative embodiment, a single steeringmechanism may be used both to deflect the distal end portion and tofurther shape the pre-shaped distal tip into the desired hook-shapedconfiguration.

[0028] In another embodiment of the present invention, the distal endpotion of the electrode catheter may be adapted to be steerable ordeflectable at three regions, namely, a distal tip deflection region, anintermediate deflection region, and a proximal deflection region. Thecurvature of the distal end portion at the intermediate deflectionregion, in addition to either or both of the distal tip deflectionregion and the proximal deflection region, enables more flexibility inconforming the shape of the distal end portion of the catheter to theshape of the target tissue, e.g., the above mentioned isthmus of tissue,during mapping and/or ablation of the target tissue. In an embodiment ofthe present invention, the intermediate deflection region is adapted tobe curved towards the target tissue, thereby to provide improved contactwith the target isthmus when the end portion of the catheter is urgedagainst the target tissue.

[0029] In yet another embodiment of the present invention, the distalend portion is not deflectable at the intermediate region but, rather,the distal end portion is formed of a resilient material and ispre-shaped to have a predetermined curvature at the intermediate region.In this embodiment of the invention, when the distal end portion isurged against the target tissue, the curvature of the intermediateregion changes until the electrode configuration on the distal endpotion conforms to the shape of the target tissue. This ensures urgedcontact between the at least one electrode and the target tissue withoutan additional steering mechanism.

[0030] According to an embodiment of the present invention, the at leastone ablation electrode is brought into secured engagement with a targettissue, for example, the isthmus of tissue between the inferior venacava and the tricuspid annulus, as follows. First, the distal end of thecatheter is guided into the right atrium. As the distal end of thecatheter advances in the right atrium, the proximal steering mechanismmay be activated to deflect the entire distal end portion, such that thedistal end portion may be conveniently inserted into the rightventricle. Once the distal end portion is inside the right ventricle,the distal steering mechanism is activated to produce the hook-shapeconfiguration at the tip of the distal end portion. Then, the catheteris pulled back, i.e., in the direction of the right atrium, until thehook-shaped tip of the distal end is anchored at the tricuspid annulus.The catheter may then be pulled further back and the curvature of thedistal end portion may be adjusted, e.g., using the proximal steeringmechanism, until the at least one ablation electrode securely engages anablation site along the isthmus of tissue between the tricuspid annulusand the inferior vena cava. Once such secured engagement is obtained,the at least one ablation electrode may be activated to produce asubstantially continuous, linear, lesion at the ablation site.

[0031] As mentioned above, a catheter having a pre-shaped distal tip mayalternatively be used. In such case, the catheter may be guided into theright ventricle and then pulled back until the pre-shaped tip isanchored at the tricuspid annulus, obviating the step of deflecting thedistal tip before pulling back the catheter. The catheter may then bepulled further back and the curvature of the distal end portion may beadjusted, e.g., using the proximal steering mechanism, as describedabove, until the distal tip assumes the desired hook-shapedconfiguration that provides a firm grip of the tricuspid annulus andsecure engagement between the at least one ablation electrode and theablation site, e.g., along the isthmus of tissue between the tricuspidannulus and the inferior vena cava.

[0032] In other embodiments of the present invention, an electrodecatheter configuration as described above may be used for mapping and/orablation of tissue at other intracardiac location where anchoring ontoan edge of an orifice may be helpful in correctly and securelypositioning an electrode catheter. For example, a configuration asdescribed above may be useful for mapping and, possibly, ablating oftissue in the vicinity of the coronary sinus, by maneuvering the distalend of the catheter into the coronary sinus and pulling the catheterback until the distal tip of the catheter is anchored at an edge of thecoronary sinus orifice.

[0033] In yet another aspect, an ablation catheter is provided andincludes a probe, an electrode mounted on the probe so as to movablerelative thereto, and remote-operated actuator means for moving theelectrode. An elongate conductor is preferably connected to theelectrode and insulation means is preferably provided around theconductor. The insulation means can comprise a tubular sheath thatextends substantially from the actuator means to the electrode and ishoused in a longitudinal channel in the probe. Axial sliding movement ofthe electrode is preferably then arranged to be effected by axialmovement of the sheathed conductor at the end thereof remote from theelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be understood and appreciated morefully from the following detailed description of the preferredembodiment taken in conjunction with the accompanying drawings in which:

[0035]FIG. 1 is a schematic, cross-sectional, illustration of a humanheart showing an atrial flutter circuit including an isthmus of tissuebetween the inferior vena cava and the tricuspid annulus;

[0036]FIG. 2 is a schematic, cross-sectional, illustration of anelectrode catheter in accordance with an embodiment of the presentinvention;

[0037]FIG. 3 is a schematic, side view, cross-sectional, illustration ofa distal end portion of the electrode catheter of FIG. 2;

[0038] FIGS. 4A-4C are schematic, front view, cross-sections of thedistal end portion of FIG. 3, taken along section lines A-A, B-B andC-C, respectively;

[0039]FIG. 5 is a schematic, cross-sectional, illustration of the humanheart, showing the electrode catheter of FIG. 2 being introduced intothe right atrium;

[0040]FIG. 6 is a schematic, cross-sectional, illustration of the humanheart, showing the electrode catheter of FIG. 2 being steered from theright atrium into the right ventricle;

[0041]FIG. 7 is a schematic, cross-sectional, illustration of the humanheart, showing the tip of the electrode catheter of FIG. 2 beingdeflected into a “hook” shape;

[0042]FIG. 8 is a schematic, cross-sectional, illustration of the humanheart, showing the electrode catheter of FIG. 2 being pulled back toengage the isthmus of tissue between the inferior vena cava and thetricuspid annulus with the tip of the catheter anchored at the tricuspidannulus;

[0043]FIG. 9 is a schematic illustration of an end portion of anelectrode catheter in accordance with another embodiment of the presentinvention;

[0044]FIGS. 10A and 10B are schematic illustrations of part of anelectrode catheter in accordance with yet another embodiment of thepresent invention, in a non-deflected configuration and a deflectedconfiguration, respectively;

[0045]FIGS. 11A and 11B are schematic illustrations of part of anelectrode catheter in yet another embodiment in which the electrode isslidable and the catheter is shown in a non-deflected configuration andin a deflected configuration; and

[0046] FIGS. 12-14 illustrate the slidable electrode in more detail withthe catheter being shown without the preformed distal tip.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] Reference is made to FIG. 2 which schematically illustrates aperspective view of an ablation and/or mapping catheter 10 in accordancewith an embodiment of the present invention.

[0048] Catheter 10 includes a handle portion 22, electric connectors 24,a tubular catheter shaft 11 and a distal end portion 12 including an endshaft 13. Distal end portion 12 includes a distal tip 16, a distal tipdeflection region 60 and a proximal deflection region 62. According tothe present invention, distal end portion 12 can be steered from agenerally straight configuration, indicated by the solid lines in FIG.1, to a deflected configuration, indicated by the broken lines inFIG. 1. The broken line configuration in FIG. 1 also illustrates howdistal deflection region 60 can be deflected into a hook-shapedconfiguration, as described in detail below.

[0049] In an embodiment of the present invention, tip 16 may include asensor or mapping electrode, as is known in the art, for monitoring theelectric potential of tissue in contact therewith. This may be helpfulin guiding and positioning distal end portion 12, as described below.Additionally or alternatively, tip 16 may include an ablation electrodefor ablating tissue in contact therewith.

[0050] Reference is now also made to FIG. 3 which schematicallyillustrates a side-view, cross-section, of distal end portion 12. Endshaft 13, which is preferably hollow as shown in FIG. 3, accommodates anelongated configuration 40 of ablation electrodes 14. Elongatedconfiguration 40 may include any number of electrodes 14, with apredetermined spacing therebetween, or a single elongated electrode, asknown in the art, adapted to produce a substantially continuous,substantially linear, lesion when brought into operative engagement witha target tissue. Electrodes 14 are preferably all ring-electrodescovering the entire circumference of shaft 13. Additionally oralternatively, electrodes configuration 40 may include at least onemapping electrode, as is known in the art, for monitoring the potentialof the tissue in contact with the electrode configuration.

[0051] Reference is now made also to FIGS. 4A-4C which schematicallyillustrate front-view cross-sections of distal end portion 12 alongsection lines A-A, B-B, and C-C, respectively, in FIG. 3. In accordancewith the present invention, catheter 10 includes a distal steeringmechanism which is used to deflect tip 16 of distal end portion 12, asmentioned above, by producing a small radius of curvature at region 60.Catheter 10 further includes a proximal steering mechanism whichcontrols the curvature of region 62, between shaft 11 and 13, thereby tocontrol the deflection of the entire distal end portion 12.

[0052] The distal and proximal steering mechanisms may include anysuitable steering mechanisms known in the art, for example, the controlmechanisms described in U.S. Pat. No. 5,383,852 to Stevens-Wright, thedisclosure of which is incorporated herein by reference. As shown inFIGS. 3-4C, the distal and proximal control mechanisms may includecontrol wires 55 and 64, respectively, which extend along the interiorof shaft 11 from handle portion 22 to regions 60 and 62, respectively,of distal end portion 12. Wire 55 is attached to tip 16 and may extendthrough middle guiding loops along most of the length of shaft 13, asshown in FIGS. 4B and 4C, and then through off-center guiding loops atregion 60, as shown in FIG. 4A, whereby only a small segment adjacent totip 16 is deflected by wire 55. Wire 64 may extends through off-centerguiding loops in shaft 13, as shown in FIG. 4C, and is attached to endshaft 13 at region 62.

[0053] The deflection of distal end portion 12 into a desiredconfiguration is preferably controlled by an electrophysiologist usingcontrol members 26 and/or 27 on handle portion 22. In the embodimentshown in FIG. 2, control member 26 may include a rotatable controlmember attached to wire 55, such that forward or backward rotation ofcontrol member 26 results in corresponding movement of wire 55, therebycontrolling the deflection of end portion 12 at region 60. Controlmember 27 may include a slidable control member attached to wire 64,such that forward or backward sliding of control member 27 results incorresponding movement of wire 64, thereby controlling the deflection ofend portion 12 at region 62. As known in the art, theelectrophysiologist may also rotate distal end portion 12 about thelongitudinal axis of catheter 10. Any suitable rotation mechanism, as isknown in the art, can be used to control the rotation of distal endportion 12. For example, catheter shaft can be made of a rotationallyrigid material that transmits the rotation of handle portion 22 todistal end 12. Alternatively, the rotation of handle 22 may betransmitted by a rotationally stiff member (not shown) extendinglongitudinally through the interior of catheter shaft 11.

[0054] In an embodiment of the present invention, electrodes 14 areaddressed, together or separately, via connectors 24, which areconnected to electrodes 14 by conductors 66. Conductors 66 may extendalong the interior of catheter shaft 11 and end shaft 13, for example,through middle guiding loops, as shown in FIGS. 4A-4C.

[0055] Using connectors 24, electrodes 14 are connected to an ablationenergizing circuit, which may be activated by user controls as are knownin the art. Upon activation, the energizing circuit energizes electrodes14 with radio frequency (RF) energy, as is known in the art. Usingseparate ablation controls, the electrophysiologist may activateelectrodes 14 together or separately (if selective ablation is desired)to ablate a target tissue, as described in detail below.

[0056] As known in the art, electrodes 14 may be associated withtemperature sensors (not shown in the drawings) which may be connectedto temperature monitoring circuitry for monitoring the temperature ofthe tissue in contact with electrodes 14. An output of the temperaturemonitoring circuitry may be visually displayed to theelectrophysiologist, as is known in the art, to provide theelectrophysiologist with on-line indication of the electrodetemperatures, which are indicative of adjacent tissue temperatures. Iftemperature sensors are used, they may be connected to the monitoringcircuitry via connectors 56 and additional conductors (not shown) incatheter shaft 11.

[0057] According to the present invention, catheter 10 is used forablating tissue on the endocardium isthmus of tissue between theinferior vena cava and the tricuspid annulus of a patient suffering fromaberrant heart activity, such as atrial flutter or fibrillation, asdescribed below.

[0058] FIGS. 5-8 schematically illustrate a procedure for introducingcatheter 10 into the right atrium and subsequently guiding distal endportion 12 to securely engage a portion of the endocardium tissue 108between the inferior vena cava and the tricuspid annulus.

[0059] As shown in FIG. 5, distal end portion 12 is first guided intothe right atrium of the patient's heart 100 from the inferior vena cava.Once catheter 10 is introduced into the right atrium, theelectrophysiologist proceeds to deflect distal end portion 12 towardsthe right ventricle 104, using the proximal steering mechanism ofcatheter 10. Distal end portion 12 enters the right ventricle via thetricuspid valve 110, as shown in FIG. 6. If necessary, end shaft 13 maybe rotated to assist in the manipulation of distal end portion 12.

[0060] After distal end portion 12 is inserted into the right ventricle,the electrophysiologist uses the distal steering mechanism to deflecttip 16 into the hook-shaped configuration described above, as shown inFIG. 7. Then, the catheter is pulled back, i.e., in the direction ofinferior vena cava 112, until a portion of the tricuspid annulus 106 isgrasped by the hook-shaped tip 16, as shown in FIG. 8.

[0061] Once tip 16 is anchored at the tricuspid annulus, the cathetermay be pulled further back and the curvature of distal end portion 12may be adjusted, using the proximal steering mechanism, until electrodes14 of elongated configuration 40 securely engage a portion of theisthmus of tissue 108 between tricuspid annulus 106 and inferior venacava 112. At this point, the electrophysiologist activates some or allof electrodes 14 to ablate a substantially continuous, substantiallylinear, lesion on the endocardial wall of the isthmus of tissue 108.

[0062] As described above, electrodes 14 may be associated withtemperature sensors. These sensors may include thermocouples or anyother temperature sensing means known in the art. Based on thetemperatures measured by these optional temperature sensors, theelectrophysiologist may deactivate some or all of electrodes 14 when thetemperature of the ablated tissue site exceeds a predeterminedthreshold. Then, when the temperature of the ablated sites drops belowthe threshold, the electrophysiologist may reactivate electrodes 14 iffurther ablation is required.

[0063] As mentioned above, tip 16 may optionally include a sensorelectrode for monitoring/mapping the electrical potential of tissueadjacent tip 16, e.g., to enable more accurate and/or more efficientpositioning of end portion 12 against isthmus of tissue 108. Sensorelectrodes may also be included in electrode configuration 40, e.g., formapping the electrical potential along isthmus of tissue 108, during orbetween ablation sessions, to determine whether further ablation may benecessary.

[0064] Reference is now made to FIG. 9 which schematically illustrates adistal end portion 212 of an ablation catheter in accordance withanother embodiment of the present invention, having an elongatedelectrode configuration 240 including a plurality of electrodes 214 anda tip 216. In the embodiment of FIG. 9, distal end potion 212 is adaptedto be steerable or deflectable at three regions, namely, a distal tipdeflection region 260, an intermediate deflection region 250 and aproximal deflection region 262. Regions 260 and 262 are generallyanalogous to the distal and proximal deflection regions 60 and 62,respectively, of distal end portion 12, as described above withreference to FIGS. 2-8. Intermediate deflection region 250 may belocated at a predetermined position along electrode configuration 240.The mechanisms for deflecting end portion 212 at regions 260 and 262 maybe similar to those used for deflecting end portion 12 at regions 60 and62, respectively, as described in detail above with reference to FIGS.2-8. The mechanism for deflecting distal end portion 212 at intermediateregion 250 may include any suitable deflection mechanism, for example, acontrol wire (not shown) extending through the hollow interior of endportion 212, analogous to control wires 55 and 64 in the embodiment ofFIGS. 2-8.

[0065] The curvature of end portion 212 at any or all of regions 260,250 and 262 may be controlled by the electrophysiologist using anysuitable controls (not shown), for example, handle controls similar tocontrols 26 and 27 in the embodiment of FIGS. 2-8. Thus, in thisembodiment, the electrophysiologist may control the curvature of distalend portion 212 at region 250, in addition to controlling the curvatureof distal and proximal regions 260 and 262. The addition of intermediatedeflection region 250 enables more flexibility in conforming the shapeof distal end portion 212 to the shape of isthmus of tissue 108 duringablation treatment. In an embodiment of the present invention,intermediate deflection region 250 is adapted to be deflected in thedirection indicated by arrow 270, so as to provide improved contact withisthmus of tissue 108 when end portion 212 is urged against the tissue.

[0066] In yet another embodiment of the present invention, end portion212 is not deflectable at region 250 but, rather, end portion 212 isformed of a resilient material and is pre-shaped to have a predeterminedcurvature at region 250, as shown generally in FIG. 9. In thisembodiment of the invention, when end portion 212 is urged against atarget tissue, such as isthmus of tissue 108, the curvature of region250 changes until electrode configuration 240 conforms to the shape ofthe target tissue. This ensures urged contact between electrodes 214 andthe target tissue without an additional steering mechanism.

[0067] In still another embodiment of the present invention, end portion212 is deflectable only at distal region 260, to assume a hook-shapedconfiguration as described above, but is not deflectable at proximalregion 262. End portion 212 may also be pre-shaped or deflectable atintermediate region 250, as described above. In this embodiment, oncethe tricuspid annulus is grasped by the hook-shaped tip of the catheter,it is primarily the backward pulling force applied by theelectrophysiologist that brings electrodes 214 into urged contact withthe target endocardial tissue.

[0068] Reference is now made to FIGS. 10A and 10B which schematicallyillustrate part of an electrode catheter 300 in accordance with yetanother embodiment of the present invention. Catheter 300 includes atubular catheter shaft 311 and a distal end portion 312 including an endshaft 313. Distal end portion 312 includes a distal tip 316, a distaltip deflection region 360 and a proximal curvature region 362. In thisembodiment, region 360 distal end portion 312 is pre-shaped to have apartly deflected configuration, as shown in FIG. 10A, with aninner-curve angle α. Such pre-shaping of region 360 may be performed bypre-baking region 360 into the desired configuration, as is known in theart. As described below, distal end portion 312 may be steered into adeflected configuration, shown in FIG. 10B, wherein proximal curvatureregion 362 is curved to a predetermined extent and distal deflectionregion 360 is further deflected into a hook-shaped configuration,similar to that described above with reference to FIGS. 2-8.

[0069] Distal end portion 312 has an elongated electrode configuration340 including a plurality of electrodes 314 and a tip 316. As in theembodiment of FIGS. 2-8, tip 316 may include a sensor or mappingelectrode, as is known in the art, for monitoring the electric potentialof tissue in contact therewith and/or an ablation electrode for ablatingtissue in contact therewith. In the embodiment of FIGS. 10A and 10B,distal end potion 312 is adapted to be steerable or deflectable by asingle deflection mechanism at both regions 362 and 360. The mechanismfor deflecting end portion 312 at regions 360 and 362 may include acontrol wire (not shown), similar to control wire 55 in FIGS. 3 and4A-4C, which extends through the hollow interior of end portion 312 .The control wire is fixedly attached to tip 316 and may extend throughoff-center guiding loops, as are known in the art, along the entirelength of shaft 313. Thus, in contrast to the embodiments describedabove with reference to FIGS. 2-8, the curvature of the entire length ofdistal end portion 312, including regions 362 and 360, is affected uponactivation of the deflection mechanism, thereby producing the deflectedconfiguration shown in FIG. 10B. re 55. In an embodiment of the presentinvention, shaft 313 is made from a material which is more flexible thanthe material used for shaft 311. The transition between the materials ofshafts 311 and 313 is indicated by numeral 315. The material for shaft313 may include Polyether Block Amide, having a Shore D hardness of40-55, available from Atochem, Inc., U.S.A., under the trade name ofPebax. It should be appreciated, however, that wide range of materialsand hardnesses of shaft 313 may be suitable for the present invention,depending on specific design requirements. The material used for shaft311 should be at least slightly harder than that of shaft 313, andpreferably has a Shore D hardness at least 5 higher than that of shaft313.

[0070] It should be appreciated that, in the embodiment of FIGS. 10A and10B, when the control wire is pulled backwards to deflect end portion312, region 362 becomes curved and region 360 is fully deflected intothe desired hook-shaped configuration, as shown in FIG. 10B. Thus, thedeflection of both regions 362 and 360 is performed in a single action,obviating the need to use two separate deflection mechanisms, as in someof the above described embodiments. This simplifies the deflectionprocedure to be executed by the electrophysiologist.

[0071] Catheter 300 may be used for mapping and/or ablating the isthmusof tissue between the inferior vena cava and the tricuspid annulus, asfollows. In analogy to the procedure described above with reference toFIGS. 5-8, distal end portion 312 is first guided into the right atriumof the patient's heart from the inferior vena cava. Once end portion 312is introduced into the right atrium, the electrophysiologist proceeds tosteer distal end portion 312 towards the right ventricle, using thesingle steering mechanism described above. Distal end portion 312 entersthe right ventricle via the tricuspid valve, in analogy to thedescription above with reference to FIG. 6. If necessary, end shaft 313may be rotated by the electrophysiologist to assist the manipulation ofdistal end portion 312.

[0072] Since distal end portion 312 is inserted into the right ventriclewith a partly deflected distal deflection region 360, there is no needto further deflect the distal end portion before anchoring tip 316 atthe tricuspid annulus. The electrophysiologist then simply pulls backthe catheter, in the direction of the inferior vena cava, until aportion of the tricuspid annulus is grasped by the partly deflected tip16, in analogy to the description above with reference to FIG. 8.

[0073] It has been found by the present inventors that when distaldeflection region 360 is pre-shaped to be partly deflected by aninner-curve angle, α, of between about 20 degrees and about 100 degrees,for example, 40-60 degrees, regions 360 and 362 assume a finalconfiguration (upon deflection), as shown in FIG. 10B, which is suitablefor mapping and/or ablating tissue in the vicinity of the tricuspidannulus as described above. This finding is empirical and may depend onvarious parameters and specific applications design requirements ofcatheter 300. For example, the choice of angle α may depend on thematerial used to form shaft 313, the distance between transition point315 and the proximal end of electrode configuration 340 (indicated bynumeral 356), the distance between the center of region 360 (indicatedby numeral 355) and distal tip 316, and/or the length of electrodeconfiguration 340. For example, an angle of 40-60 degrees has been foundsuitable for a distal end portion 312 made from the Pebax materialdescribed above, wherein the distance between transition 315 andproximal electrode 356 is approximately 3.5 cm, the distance betweencenter 355 and tip 316 is approximately 1.8 cm, and the length ofelectrode configuration 340 is approximately 2.8 cm.

[0074] Once tip 316 is anchored at the tricuspid annulus, the cathetermay be pulled further back and the deflection mechanism described abovemay be used to further curve region 362 and to fully deflect region 360into the hook-shaped configuration shown in FIG. 10B, until electrodes314 of elongated configuration 340 securely engage a portion of theisthmus of tissue between tricuspid annulus and inferior vena cava. Atthis point, the electrophysiologist may activate some or all ofelectrodes 314 to ablate a substantially continuous, substantiallylinear, lesion on the endocardial wall, as described above.

[0075] With reference to FIGS. 11A and 11B which schematicallyillustrate part of an electrode catheter 400 in accordance with yetanother embodiment. The catheter 400 includes a tubular catheter shaft411 and a distal end portion 412 including an end shaft 413. Distal endportion 412 includes a distal tip 416, a distal tip deflection region460 and a proximal curvature region 462. In this embodiment, region 460of distal end portion 412 is pre-shaped to have a partly deflectedconfiguration, as shown in FIG. 11A, with an inner-curve angle α. Suchpre-shaping of region 460 may be performed by pre-baking region 460 intothe desired configuration, as is known in the art. As described below,distal end portion 412 may be steered into a deflected configuration,shown in FIG. 11B, wherein proximal curvature region 462 is curved to apredetermined extent and distal deflection region 460 is furtherdeflected into a hook-shaped configuration, similar to that describedabove with reference to FIGS. 2-8.

[0076] Distal end portion 412 includes at least one elongated electrode440. As in the embodiment of FIGS. 2-8, tip 416 can include a sensor ormapping electrode, as is known in the art, for monitoring the electricpotential of tissue in contact therewith and/or an ablation electrodefor ablating tissue in contact therewith. In the embodiment of FIGS. 11Aand 11B, distal end potion 412 is adapted to be steerable or deflectableby a single deflection mechanism at both regions 462 and 460. Themechanism for deflecting end portion 412 at regions 460 and 462 mayinclude a control wire (not shown), similar to control wire 55 in FIGS.3 and 4A-4C, which extends through the hollow interior of end portion412 . The control wire is fixedly attached to tip 416 and may extendthrough off-center guiding loops, as are known in the art, along theentire length of shaft 413. Thus, in contrast to the embodimentsdescribed above with reference to FIGS. 2-8, the curvature of the entirelength of distal end portion 412, including regions 462 and 460, isaffected upon activation of the deflection mechanism, thereby producingthe deflected configuration shown in FIG. 11B. In an embodiment of thepresent invention, shaft 413 is made from a material which is moreflexible than the material used for shaft 411. The transition betweenthe materials of shafts 411 and 413 is indicated by numeral 415.

[0077] In this embodiment, the at least one electrode 440 is of a typedisclosed in commonly assigned, U.S. patent application Ser. No.09/832,548, which is hereby incorporated by reference in its entirety,and includes a tubular electrode 440 mounted on the catheter 400 so asto be axially slidable relative thereto. The catheter 400 includesremote-operated actuator means (shown in FIGS. 12-14) for causing theelectrode 440 to slide in the axial direction. The means thus comprisesanother mechanism that is included in the catheter 400 for causingmovement of the electrode 440 under the direction of a surgeon or thelike.

[0078] Similar to the electrode catheter 400 of FIGS. 11A and 11B, theelectrode catheter 500 can be used for mapping and/or ablating theisthmus of tissue between the inferior vena cava and the tricuspidannulus. The method of operating of the electrode catheter 500 issimilar to the method of operating the catheter 400 with the exceptionthat the at least one electrode 440 is moved in a sliding manner bymanipulation of the remote-operated actuator means.

[0079]FIGS. 12 through 14 illustrate several embodiments of slidingelectrode 440 and more specifically, several mechanisms for effectuatingthe sliding of the electrode 440 are illustrated. For ease ofillustration, these mechanisms are described with reference to acatheter having a simpler construction in that the catheter does notinclude the pre-formed distal tip. However, it will be appreciated thatany of these mechanisms can be used to causing the sliding action of theelectrode 440 illustrated in FIGS. 11A and 11B in combination with apre-formed distal tip.

[0080] With reference to FIG. 12, an ablation catheter 500 for use inheart surgery comprises a probe 502, a tubular electrode 440 mounted onthe probe 502, so as to be axially slidable relative thereto, andremote-operated actuator means 504 for so sliding the electrode 440.

[0081] The catheter 500 also includes a flexible tube or shaft 505forming an extension of the probe 502. The flexible tube/shaft 505 andthe probe 502 are of electrically-insulating material, and comprise adistal tip 506, an axially-extending shaft 507 and a rear end portion508 to which the flexible tube 505 is attached. A surface groove orchannel 509 is formed in the end portion 508 and shaft 507, and extendslongitudinally up to the tip 506, or near to the tip 506.

[0082] The channel 509 locates a conductor 510 which interconnects theelectrode 440 with a controllable source 515 of (in this example) radiofrequency energy. The conductor 510 is enclosed in an insulating sheath516 of flexible construction. The flexible sheath 516 and the conductor510 there are axially slidable within the channel 509 of the catheter500. This provides for electrical insulation of the conductor 510 as theelectrode 440 is moved along the probe shaft 507. The conductor 510 andsheath 516 are long enough to allow for this movement of the electrode440.

[0083] The illustrated electrode 440 is of tubular and cylindrical form(but in alternative embodiments could be ovoid, spherical or othergeometry) so that it is slidable along the probe shaft 507, as indicatedby the double-headed arrow 518. The material of the electrode 440 is ofan electrically-conducting metal or alloy.

[0084] The actuator mechanism 504 which provides for movement of theelectrode 440 is connected to the conductor 510 by means of a slidingmechanism, ratchet mechanism (for example worm screw attachment to theterminal portion of the conductor 510) or other mechanism so thatoperation of this actuator causes axial displacement of the conductor510 and thereby axial displacement of electrode 440, which is movedalong the probe shaft 507 toward the end portion 508 from an initialposition closer to the tip 506, or vice versa.

[0085] The portion of the probe over which the electrode 440 isdisplaced can be coated with a hydrophobic or similar substance in orderto lubricate the displacement of the catheter.

[0086]FIG. 13 shows an example of a suitable ratchet mechanism 527,which comprises a worm screw 540, the teeth of which are engaged by aworm wheel 541, whereby manual rotation of the wheel causes axialdisplacement of the worm screw 543 and thereby corresponding axialmovement of the conductor 510 and the electrode 440.

[0087] Using conventional technology in the construction of deflectableablation catheters, the portion of the probe shaft 507 over which theelectrode 440 slides, can be flexed, extended, or rotated by axial orrotational displacement of a collar 542 fixed to the actuator mechanism504, as indicated by the double headed arrows 526 a, 526 b.

[0088] In an alternative arrangement, a replaceable stylet 520 can befitted in the end portion 508 of the probe 507. This allows a range ofstylets having different end curvatures to be introduced into the endportion 508 and advanced to the probe tip, so as to produce curvaturesof that portion of the probe shaft 507 over which the electrode slides.It will be appreciated that the actuating means 504 or 527, like thesource 515, are located remote from the catheter tip 506.

[0089] In the application of the invention, the catheter 500 is employedto create long endocardial lesions in cardiac chambers or longepicardial lesions on the outer surface of the cardiac chambers byapplication of radio frequency current provided by the source 515.Contiguous lesions are created, in a series of steps, by careful,remote-operated movement of the electrode 440, and delivery of energythereto (from source 515) at each position.

[0090] Temperature control during lesion production can be effected byusing standard components, such as thermocouples or thermisters,embedded in the electrode 440 or in a catheter shaft disposed nearby.

[0091] In an alternative embodiment, direct current or other energy canbe employed as an alternative to alternating radio frequency current.Other suitable forms of heat energy comprise laser energy and microwaveenergy. In FIG. 14, parts corresponding to those of the embodiment ofFIG. 11 have been given like reference numerals. In the alternativeembodiment of FIG. 14, instead of groove 509, the conductor 510 extendsthrough an axially retractable insulation collar 502 a which slides overthe shaft of the catheter 500. As shown in FIG. 14, the collar 502 aabuts with electrode 440 and is retractable in part within an annularblind bore 530 in the end portion 508 on leftward movement in FIG. 14 ofthe electrode from the initial position, shown. This is intended tofacilitate easier assembly of the ablation catheter.

[0092] It should be understood that electrode catheter configurations asdescribed above may also be used for mapping and/or ablation of otherintracardiac sites where anchoring onto an edge of an orifice may behelpful in correctly and securely positioning an electrode catheter. Forexample, a configuration as described above may be useful for mappingand, possibly, ablating tissue in the vicinity of the coronary sinus, bymaneuvering the distal end of the catheter into the coronary sinus andsubsequently pulling the catheter back until the distal tip of thecatheter is anchored at an edge of the coronary sinus orifice.

[0093] It will be appreciated by persons skilled in the art that thepresent invention may be carried out using any of the above describedconfigurations of electrodes and/or deflection regions and/or pre-shapedregions.

[0094] It should be appreciated that the present invention is notlimited to the specific embodiments described herein with reference tothe accompanying drawing. Rather, the scope of the present invention islimited only by the following claims:

1. A catheter for ablating intracardiac tissue comprising: a bodyportion; a distal end portion having a distal tip and accommodating atleast one ablation electrode adapted to produce a substantiallycontinuous, elongated, lesion in said tissue when energized with radiofrequency (RF) energy; a distal steering mechanism which controls thecurvature of a region of said distal end portion near said distal tip,wherein said distal steering mechanism is adapted to deflect said distaltip from a first, generally straight, configuration into a second,hook-shaped, configuration; a proximal steering mechanism which controlsthe curvature of a proximal region of said distal end portion, whereinsaid proximal steering mechanism is adapted to deflect substantially theentire length of said distal end portion wherein the distal end portionincludes a pre-shaped, curved region at a predetermined location alongsaid elongated configuration of electrodes; and an intermediate steeringmechanism which controls the curvature of a region of said distal endportion along said at least one ablation electrode.
 2. A catheteraccording to claim 1, wherein guiding said distal end portion comprisesdeflecting said catheter at a proximal region of said distal endportion.
 3. A catheter for mapping and/or ablating tissue comprising: abody portion; a distal end portion having a distal tip and including atleast one distal end portion electrode proximal to said distal tip, saidat least one distal end portion electrode adapted to produce asubstantially continuous, elongated, lesion in said tissue whenenergized with radio frequency (RF) energy; a proximal deflectionmechanism for deflecting substantially the entire length of said distalend portion in a predetermined direction and including at least aportion of the length of said proximal deflection mechanism locatedinside said body portion wherein said proximal deflection mechanism is afirst pull wire; and a distal deflection mechanism for deflecting aregion of said distal end portion including said distal tip in saidpredetermined direction, from a generally straight configuration into ahook-shaped configuration, and at least a portion of said distaldeflection mechanism being located inside said body portion, whereinsaid distal deflection mechanism is a second pull wire and wherein saidat least one distal end portion electrode is located proximal to theregion deflected by said distal deflection mechanism, wherein saidregion near the distal top of the distal end portion is pre-shaped toassume a first configuration.
 4. A catheter for mapping and/or ablatingtissue comprising: a body portion; a distal end portion having a distaltip and including at least one distal end portion electrode proximal tosaid distal tip, said at least one distal end portion electrode adaptedto produce a substantially continuous, elongated, lesion in said tissuewhen energized with radio frequency (RF) energy, said distal tipincluding a distal tip electrode; a proximal deflection region betweensaid body portion and said distal end portion; a distal deflectionregion near the distal tip of said distal end portion and in betweensaid at least one distal end portion electrode and said distal tipelectrode; a proximal deflection mechanism for deflecting said proximaldeflection region and including at least a portion of the length of saidproximal deflection mechanism located inside said body portion; and adistal deflection mechanism for deflecting said distal deflection regionand including at least a portion of the length of said distal deflectionmechanism located inside said body portion, wherein said proximaldeflection region and said distal deflection region are deflected in thesame direction, wherein said region near the distal tip of the distalend portion is pres-shaped to assume a first configuration which is apartly deflected configuration.
 5. A catheter for mapping and/orablating tissue comprising: a body portion; a distal end portion havinga distal tip and including at least one distal end portion electrodeproximal to said distal tip, said at least one distal end portionelectrode adapted to produce a substantially continuous, elongated,lesion in said tissue when energized with radio frequency (RF) energy,said distal tip including a distal tip electrode; a proximal deflectionregion between said body portion and said distal end portion; a distaldeflection region near the distal tip of said distal end portion and inbetween said at least one distal end portion electrode and said distaltip electrode; a first pull wire having a proximal end and a distal end,said distal end of said first pull wire being connected to a first pointinside said distal tip and said first point being radially remote from apoint on the central axis of said catheter; and a second pull wirehaving a proximal end and a distal end, said distal end of said secondpull wire being connected to a second point inside said proximaldeflection region and said second point being located on an axis whichis parallel to the central axis of the catheter and on which the firstpoint is located, whereby deflection of the proximal deflection regionand the distal deflection region are in the same direction, wherein saidregion near the distal tip of the distal end portion is pre-shaped toassume a first configuration.
 6. A method of treating cardiacarrhythmia, comprising: guiding a distal end portion of a catheter, thedistal end portion having a distal tip that is pre-shaped to assume afirst configuration and accommodating at least one elongated ablationelectrode, from the inferior vena cava into the right atrium of a humanheart; guiding said distal end portion from the right atrium into theright ventricle of said heart; pulling said catheter towards theinferior vena cava until said distal tip engages the tricuspid annulusof said heart and said at least one elongated electrode engages theisthmus of tissue between the tricuspid annulus and the inferior venacava of said heart; deflecting said distal tip from said firstconfiguration into a hook-shaped configuration; and activating said atleast one elongated electrode to produce a substantially continuouslesion on said isthmus of tissue.
 7. A method according to claim 6,wherein guiding said distal end portion from the right atrium into theright ventricle includes deflecting said catheter at a proximal regionof said distal end portion.
 8. A method according to claim 6, furtherincluding the step of: manipulating an intermediate steering mechanismto control a curvature of a region of said distal end portion along saidat least one elongated electrode.
 9. A method of treating cardiacarrhythmia and/or mapping intracardiac tissue, comprising: guiding adistal end portion of a catheter, the distal end portion having a distaltip that is pre-shaped to assume a first configuration and accommodatingat least one elongated ablation electrode into an intracardiac region;pulling said catheter backwards until said distal tip engages an edge ofan intracardiac orifice and said at least one elongated electrodeengages a target tissue in the vicinity of said intracardiac orifice;deflecting said distal tip from the first configuration into thehook-shaped configuration; and mapping and/or ablating a portion of saidtarget tissue using said at least one elongated electrode.
 10. A methodaccording to claim 9, wherein guiding said distal end portion comprisesdeflecting said catheter at a proximal region of said distal endportion.
 11. A method according to claim 9, further including the stepof: manipulating an intermediate steering mechanism to control acurvature of a region of said distal end portion along said at least oneelongated electrode.
 12. A catheter for mapping and/or ablating tissuecomprising: a body portion; a distal end portion having a distal tip andincluding an ablation segment proximal to said distal tip for ablatingtissue, said ablation segment adapted to produce a substantiallycontinuous, elongated, lesion in said tissue when energized with radiofrequency (RF) energy; a proximal deflection mechanism for deflectingsubstantially the entire length of said distal end portion in apredetermined direction and including at least a portion of the lengthof said proximal deflection mechanism located inside said body portionwherein said proximal deflection mechanism is a first pull wire; and adistal deflection mechanism for deflecting a region of said distal endportion including said distal tip in said predetermined direction, froma generally straight configuration into a hook-shaped configuration, andat least a portion of said distal deflection mechanism being locatedinside said body portion, wherein said distal deflection mechanism is asecond pull wire and wherein said ablation segment is located proximalto the region deflected by said distal deflection mechanism, whereinsaid region near the distal top of the distal end portion is pre-shapedto assume a first configuration.